Guitarists use electronic tuners to adjust the instrument to a standard or selected reference pitch, and can place capos in various positions on the guitar neck to change the pitch of all the strings on the instrument. Capos allow the use of chords or different chord versions that would not be available to the musician if he tried to play them without the capo. The use of a capo enables the musician to use chords in positions that include more open string combinations. Open strings tend to have unique sound characteristics that are desirable in many musical situations.
For ideal performance, the musician should re-tune the instrument after repositioning the capo. Many performers will take the stage with both a capo and a tuner in hand. This can be cumbersome to the artist and distracting to the audience.
There are many types of tuners available on the market. Each one directly or indirectly senses the vibrating string, processes the sensed audio signal to determine the closest corresponding note, and then compares the actual pitch of the string to the target tuning pitch. A display interface shows the user if the note is flat or sharp and the user tunes the string until he gets and in-tune indication from the tuner display. Tuner displays are typically LED lights, an analog needle mete, or an LCD or other digital graphic display device.
The audio signal from the instrument can be input into the tuner three ways. Some tuners have an input jack to directly wire the instrument to the tuner. Electric guitars or acoustic guitars with pickups (built in magnetic, piezo or microphone sensors) can be wired directly into the tuner. Some tuners use a built in microphone to pick up the signal. This is effective in quiet room conditions and for acoustic instruments. Noisy settings such as concert halls, studios, classrooms, and the like make it difficult to use a tuner in microphone mode. Some tuners clamp onto the instrument and utilize a built in sensor (usually a piezo type pickup) to pick up the vibrations in the guitar neck.
A plugged in version is the most efficient as the input signal is directly coupled to the input circuit of the tuner and no ambient noise will affect the sensitivity or accuracy of the signal recognition. The disadvantages are that the tuner must be plugged in. This can be an inconvenience or simply not possible in certain stage, recording or practice conditions. Serious musicians are reluctant to run their signal through a tuner and then into their amplification devices because deterioration of the audio signal is always possible when additional devices are wired into the signal path.
Tuners with a microphone input can be very effective also, but ambient room noise can confuse the input circuitry of the tuner giving erroneous readings. Using a microphone input tuner in a stage or studio environment is not practical.
Clip-on type tuners that use a sensor and pick up the vibrations from the guitar body can be very effective. If designed properly they can be as sensitive as a direct wired version and can work well in noisy environments. They are also very convenient. They can be kept in a pocket or clipped on to the headstock of the guitar when not being used.